1. Field of the Invention
This invention relates generally to optical image recognition. More particularly, the present invention relates to an image recognition apparatus which is used for optically checking an inspection object such as electronic device, printed circuit board, and so on.
2. Description of the Prior Art
For quality control, it is necessary not only to check the performance of an electronic component but also to check the component with regard to its appearance, dimension, mounting state on a printed circuit board, and so on. For instance, a small outline package IC device requires checking with regard to the length, pitch and shape of the leads projecting from both sides of the resinous package.
Conventionally, the external checking of an electronic component is typically performed by using an optical image recognition apparatus. Now, for conveniently explaining the problems to be solved by the present invention, reference is made to FIGS. 6 and 7 of the accompanying drawings. FIG. 6 shows a prior art image recognition apparatus, whereas FIG. 7 shows a small outline package IC device to be optically inspected by the image recognition apparatus.
In FIG. 7, the IC device is shown to have a resinous package M and paired arrays of leads A1-A5, B1-B5 projecting from both sides of the package. Obviously, it is necessary to perform external checking for both arrays of leads.
As shown in FIG. 6, the prior art image recognition apparatus comprises a transparent glass support 100 for supporting thereon the IC device (inspection object), a positioner 101 for horizontally moving the support 100, an illuminator 102 for illuminating the IC device from below, and an image pickup unit (camera) 103 having a microscope. The image recognition apparatus further comprises a central processing unit (CPU) 104 connected to the image pickup unit 103, and a monitor display 105 connected to the CPU. The CPU controls the positioner 101 and the illuminator 102.
As shown in FIG. 7, the image pickup unit 103 provides a visual field 106, whereas the monitor display 105 provides a smaller display field 107. Thus, in order to simultaneously check and monitor the respective arrays of leads A1-A5, B1-B5, the entire image of the IC device must be contained within the display field 107.
As is well known, the resolution of the image pickup unit 103 increases as the magnification of the employed lens system increases, so that higher inspection accuracy will result. On the other hand, higher magnification of the lens system will result in reduction of the visible area within the limited visual field 106 of the image pickup unit 103.
Thus, in the case of checking the respective lead arrays located on both sides of the IC device, one lead array may come out of the visual field 106 (the display field 107 as well) if the image pickup unit 103 employs a high magnification lens system for increasing the image resolution (inspection accuracy), as shown in FIG. 7. In this case, it becomes necessary to perform lead checking twice at two different positions, which requires positional readjustments of the support 100. Further, the CPU 104 must have an additional control function of determining whether the new image taken after positional readjustment is really that of the same IC device.
It is, of course, possible to reduce the magnification of the employed lens system for simultaneously checking the respective lead arrays of the IC device. However, such a solution is inevitably accompanies by deterioration of inspection accuracy.